Dual rotor wind power assembly (variants)

ABSTRACT

The invention relates to propeller-type horizontal-axis wind turbine assemblies. All of the present assembly variants comprise, mounted on a tower, a wind turbine with two coaxial wind propellers on a rotating platform, a gearbox, systems for controlling the pitch angles of the blades and the position of the platform, and an electric generator. The design of the assemblies additionally includes improvements which make it possible to increase the efficiency with which the energy of the wind is utilized, increase electricity output, reduce service time, simplify manufacture and use, increase reliability and working life, and eliminate infrasound.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a national stage application in USA ofPCT application PC/RU2014/000579 filed on Aug. 7, 2014 claiming priorityto Russian patent application RU 2014129095 filed Jul. 16, 2014, all ofwhich incorporated herein by reference.

FIELD OF INVENTION

The invention relates to a propeller type wind turbine installationswith horizontal axis.

BACKGROUND

Existing powerful wind turbines have a turbine with three blades and arotor. Each blade is attached to the hub via the large diameter rollbearing. This design does not allow to increase the number of blades inthe rotor. Turbine having more than three blades in the bush does notrun. The three-blade turbines have low efficiency of wind power, whichis about 26%.

There are several reasons for the decline of efficiency. The main reasonis that there is a preconceived assumption that Wind Turbine Powerdepends weakly on the number of blades and depends only on the sweptarea of the blades. When designing the turbine curve the Betz diagram isused and his postulate of the theoretical maximum ratio of wind energywhich is equal to 0.59:2:6. FIG. 1 shows the theoretical curves of windenergy efficiency of an ideal wind turbine: ξ—wind energy efficiency:V₁, V₀—wind (air) flow rate through the wind turbine and at the turbineinlet. A. Betz in his dissertation considered changing the air flowkinetic energy in the profiled air channel with conditional walls. Hedid not take into account the mass-energy exchange with ambient airturbine air flow. The reduced efficiency of a rotor three-blade turbinestill occurs due to the fact that the rotating air stream appears afterthe rotor which reduces the value of an air pressure drop in the rotorthus reducing the turbine output power.

A small number of blades leads to emergence of low-frequency airpressure pulsations. The pulsation frequency is in the zone of dangerousinfrasound 0÷12, Hz. Pulsations in the single rotor turbine arise atmoments of a blade passing past the tower.

Typically a human ear perceives pulsation within the range of 16-20000Hz. Its unpleasant consequences does not only cause an excessive noisein the audible pulsation range but generate the unperceivable infrasoundin the human hearing within the range from 16 Hz to 0.001 Hz. Infrasoundcauses nervous stress, malaise, dizziness, changes in the internalorgans, especially in the nervous and cardiovascular systems. The mostdangerous is the infrasound range from 6 to 9 Hz. Significantpsychotropic effects are manifested most strongly at the frequency of 7Hz which is consonant with the alpha rhythm of the natural oscillationsof the brain. Any mental work in this case is impossible. The sound oflow intensity causes nausea and ringing in the ears, blurred vision andirrational fear. Medium intensity infrasound causes the frustration ofdigestive organs and the brain giving birth to a paralysis, generalweakness, and sometimes a blindness.

Pressure pulsation and therefore the speed deviation result in some lossof turbine power due to the reducing cyclic pressure differential acrossthe turbine wheel. The loss of power could be as high as 2-5% of itstheoretical value. The experimental results published by theMassachusetts University show that the significant part of the soundenergy is in the audio frequency range from 0 to 20 Hz, as shown inExample 3. Therefore, from both the economic and environment protectionviewpoints it is advisable to eliminate the infrasound.

Conventional technical solutions for the elimination of the cause of thelow-frequency oscillations at the wind turbines (wind powerinstallations) are increasing the number of blades or an increasing therotation speed of the wind wheel.

The double-rotor turbine rotors generally rotate in opposite directions.Their pressure pulsation frequency is higher than that of a single rotorturbine. The infrasound does not depend on the influence of the towerdoes. However, the pressure pulsations occur from the influence of theblades of one rotor on the blades of the other one. The freelyselectable number of blades in the rotors can lead to an effect ofacoustic beat. Therefore, the number of rotor blades Should not obey tothe same multiplication factors. For example: one row of blades has fourblades, the second row has two blades. Their total multiplier is 2.Similarly, one rotor has six blades and the other one has three. Theirtotal multiplier is 3. In both cases the infrasound in the 4-6 Hzfrequency range shall be generated.

The acoustic beat phenomenon can be eliminated if the number of bladesin one rotor is equal to Z, and in the other is (Z+1).

The wind turbine is known according to the patent application [JP2005036749 A 10 Feb. 2005], where:

-   Claim 1. The horizontal axis turbine rotor with variable speed and    rotatable in azimuth, depending on the wind speed. The wind turbine    provided with the means for measuring and recording the azimuth    angle, rotation speed and the noise measurement system for recording    time and frequency.-   Claim 2. Wind turbine according to claim 1, with rotor speed    controls.-   Claim 3. Wind turbine according to claim 1, where the speed control    is performed at the particular moment of time.-   Claim 4. Wind turbine according to claim 1, where the controller    device controls the azimuth angle of the rotor speed depending on    the low-frequency noise.-   Claim 5. Wind turbine according to claim 1, where the speed control    is performed in the specific area at the turbine leeward or windward    side.-   Claim 6. Wind turbine according to claim 1, where the rotation speed    is reduced at the particular time in the particular area for    suppressing the low-frequency noise.

In the patent application JP 2005036749 A, both the claims and in thedescription refer to the low-frequency noise. This invention does notcomprise any relation to the method for the prevention or elimination ofinfrasound. The method is offered to reduce the action of low-frequencynoise on a specific area by the rotation of the noise exposure vector orby reducing the wind turbine rotation speed or its operating hours.

There are the two different notations of «infrasound» and thelow-frequency noise.

Presently, the generation of infrasound by all wind turbines is aserious environmental problem.

Patent RU 2463475 C2 10 Oct. 2012 represents the wind power plantcomprising the wind turbine placed on a tower, the two coaxialmulti-blade propellers with a horizontal axis and a rotary body, anelectric generator and a step-up gear. The step-up gear is connected tothe shaft of the electric generator and the propellers shaft. Thepropellers control system controls the installation angles of theblades. The propellers are mounted at the same side of the rotationalaxis on their coaxial shafts and they are provided with the number ofblades selected on the condition z₁·z₂≤f/ω_(c), where z₁ and z₂ are thenumber of blades if the first and the second propeller, respectively; fis a safe infrasound frequency which is at least 10 Hz; ω_(c)=ω₁+ω₂ isthe relative rotation speed of the wind turbine, and ω₁ and ω₂—thefrequency of rotation of the first and second propeller, rps.

The disadvantages of this system are as follows. The formula for theoptimization of the number of blades which is aimed to avoid theemergence of infrasound does not account for the possibility of acousticbeat in the infrasound frequency range. Acoustic beat can occur due tothe coincidence of the phase position of two or more blades.

The conventional wind power plants from which the generated electricityis transmitted to an electrical network implement usually the alternatecurrent three-phase current generators. Their diversity is reduced totwo types, namely, the synchronous generators and asynchronousgenerators. In both cases, as a rule, the mechanical step-up gear shouldbe installed between the wind turbine and the electric generator.Qualitative characteristics of generated electric current and optimumuse of wind power requires a constancy of the power generator rotorspeed. Constant speed is easily established if the wind speed is eithernominal or above nominal. This occurs due to the automatic positioningof the turbine blades. If the wind speed is reduced to 10 m/s and below,maintaining a constant the number of revolutions of the generator shaftbecomes a problem. The wind turbines usually have an additional complexelectronic equipment in the form of a frequency converter, its output isvery consistent with the frequency harmonic of the electric powernetwork.

The double-rotor installations the planetary gears are mostly used asstep-up gears, which are installed in the wind, turbine transmissionbetween the propellers and the electric generators. Planetarytransmission having three movable shaft are commonly referred to as thedifferentials.

All existing differentials obey one and the same general rule. At aconstant rotation speed of one certain shaft the rotating speeds of allother shafts depend on the torque applied to each such shaft. If thenumber of revolutions of the shaft increases, the rotation speed ofother shaft is reduced, and vice versa. Let us consider the use of sucha differential in the counter-rotating wind turbine. The reducing thewind speed causes the lower wind energy imposed on the turbine blades.The speed of turbine rotors begins to decline. The blade angle automaticcontrol installation slows down the speed reduction, but it cannotrestore this speed to its to initial value.

These processes are shown for convenience in FIGS. 2 and 3.

FIG. 2 shows decrease of the turbine speed with a decrease of the windspeed.

FIG. 3 shows variation of the speed of a special three-shaft planetarymechanism (the differential).

With the decrease of wind speed causes the turbine speed decreases, thespeed of the second rotor 2 decreased less intensively than that of thefirst rotor 1 (which is explained by FIG. 2). When the speed of anyrotor, for example, the first rotor 1 falls, than in order to maintainthe generator speed at the nominal constant level it is necessary toincrease the speed of the second shaft 2 (which is explained by FIG. 3).But this is impossible, since the energy of the air flow with thedecreasing wind speed is also reduced.

If the rotor speed of the generator decreases according to thedecreasing wind speed, the generator automatically switches to anelectric motor mode powered from the central power supply network.Generation of electricity is stopped. This usually occurs at wind speedslower than 20-25% of the nominal value.

The device is necessary that would support the momentum of the generatorat the lowest possible wind speeds, which would provide a high poweroutput.

The wind turbine is known under the patent application FR 2589201A1 30Apr. 1987. The wind turbine with two rows of counter-rotating rotors,where the claim 1 comprises:

-   -   1) a supporting tower;    -   2) two freely rotating rotors with blades and their position        control mechanism;    -   3) the propeller control unit which utilizes the wind energy for        the rotation of the blades.

Claim 2 of the same patent comprising the wind turbine according toclaim 1, where the propeller control unit utilizes a pair of ball screwpair.

Claim 3 of the same patent comprising the wind turbine according toclaims 1 and 2, with the mechanisms which convert the longitudinalmovement of the propeller control unit into circular motion of the bladepins.

Claim 4 of the same patent according claims 1, 2, 3 where the upper(front) rotor rotates freely relative to the lower (rear) rotor, whilethe lower rotor is freely rotatable relative to the output shaft.

However, this structure does not correspond to the above statement.Upper and lower rotors are linked with gear-coupling with fixed axes.Therefore, the rotors cannot rotate freely at all. The torque from theupper rotor is applied with the gear transmission to the lower rotor,and only after that it is applied with the gear transmission to theoutput shaft.

Such kinematics has only one degree of freedom and therefore, thefunctional twin-rotor system turns into a single-rotor one with thedependent constrained rotors rotating in opposite directions. A stop ofany element stops the entire system. Thus it is physically impossible tomaintain a constant rotor speed using the positioning of the blades whenthe wind speed changes.

In the patent application FR2589201A1, in claim 5, the gear driveaccording to claim 4 is disclosed between the upper and the lower rotorsand the output shaft.

The description contains certain phrases, e.g., « . . . it contributesto maintaining the rotation speed of the rotors irrespective of changesof the wind speed»; «nearly constant rotor speed»; «This is facilitatedby the rotation of the blades around their axes», etc. Such statementsare the result of the general discussion. The proposed design scheme ofthe transmission from turbine rotor to the shaft can not provide theconstant output shaft speed.

Wind turbine under the patent US 2006/0093482 A1 4 May 2006 is known.This twin-rotor turbine has coaxial rotors. The set includes a planetarytype step-up gear and a special braking mechanism for the entire system.

The turbine utilizes a simple planetary satellite gear. Reducing thewind speed below the nominal, to approximately 20%, the rotation speedof all rotors is also reduced. Accordingly, the rotation speed of thegenerator is also reduced with all adverse effects.

The patent application JP 2007321659 A 13 Dec. 2007 describes thedouble-rotor installation in which the coaxial 3-blade rotors rotate inthe same direction. Actually there is only one rotor in which theturbine wheel is turned relative to the other wheel to a certain angledepending on the wind speed. It is assumed that this method can achievehigher efficiency of wind energy. The mechanism is disclosed for turningone rotor to a certain angle relative to the other wheel.

However, the double-rotor turbine comprises a serious structuralproblem, namely, the inner shaft is thinner than the outer shaft. Toprevent the physical contact of the rotors when the nacelle turns aroundits axis and the tower, the inner shaft should be extended. It resultsin the increased distance between the rotors. The deflection of theshaft increases, its strength decreases.

The layout of the existing wind turbine installations is mostly thesame. The power generator is installed in the nacelle. The nacellerotates on the axis of the tower depending on the wind direction. Fromthe generator the cable is passed down along the fixed tower. When thenacelle rotates the cable is twisted. It is necessary either to do anyautomation for cable counter-twisting with the rotation of the nacelleor install special current collectors in the cable cut. In any case, itis a problem that reduces the reliability of the system, which increasesthe cost of installation and its maintenance.

A brief review of the existing wind turbines shows the followingdisadvantages:

-   -   a) low efficiency of the use of the wind (airflow) energy in        comparison with gas or hydro turbines;    -   b) generation of infrasound, of a low frequency sound in the        range 0-12 Hz;    -   c) failure to maintain the constancy of the electric generator        rotor speed at lower wind speeds below 20% of its nominal speed.        This is usually below 8 m/s:    -   d) twisting of the main power cable by the nacelle rotating on        the stationary tower.

The technical result is the better use of wind enemy, the increase inelectricity generation, shorter maintenance intervals, versatility ofmanufacture and operation, increased reliability and service life.

SUMMARY

The technical result is achieved by using each of double-rotor windturbines.

FIGS. 4 and 5 show the embodiment of double-rotor electric powerinstallations which offers new solutions different from the conventionalones.

The wind turbine comprises a tower 1, the beating on which the whichturntable 2 is installed. On the turntable there are two coaxial rotorwind turbines, mechanical gear step-up gear, three-shaft step-up gearand the generator on a separate platform or fixed to the top of thetower.

Each turbine rotor consists of a shaft 9, 10, on one end of which thepropeller hub 3 is fixed with blades 4 and 5 and the systems for thepositioning (axial rotation) of the blades 8, the other end of the shaftis connected to the input shaft of the step-up gear 13. The rotors aremounted on the bearings 6, 11, 12. The front internal shaft bearing 6 islocated in a special spacer 7 which is connected to the second flange ofthe propeller hub, which is one of the distinctive features of thestructure. To maximize the energy of the wind the blades of the firstrotor are automatically positioned by the commands of an angle settingcontrol system, these commands correspond to the wind speed at any givenmoment. The blades of the second propeller are positioned, i.e., theyare set to the angle which keeps constant the power generator rotationspeed. Each turbine speed decreases with the decreasing wind speed, andincreases with the increasing wind speed. This speed change algorithm isset with the three-shaft gear 16, which kinematic scheme is designed asa «negative» differential unit.

The movement and the torque from the wind turbine are applied with thestep-up gear 17 via two coaxial rollers 14 and 15 to two input shafts ofthe three-shaft gear 16 and then through the combination of thetransmission shaft 17 (FIG. 4), the angular gear 18 and coupler 19 therotation speed and torque are transferred to the electric powergenerator 20.

The power generator 20 in the embodiment of double rotor electric powerinstallation (FIG. 4) is mounted on the top of the tower. The stator ofthe electric generator is wixed with the bracings to the walls of thetower.

An electric drive in the double-rotor embodiment, when it is placed onthe turntable (see FIG. 5) is taken from the output shaft of thethree-shaft gear 16. The power generator is placed horizontally, itrotates together with the turntable.

The step-up gear is a gear mechanism which kinematic scheme provides anindependent power transmission and motion of each turbine to the summingthree-shaft gearbox. The step-up gear circuit is shown in FIG. 6. Thisis the novel dual mechanism comprising the double-rotor wind turbines.

The low-speed shafts 3, 4 of the step-up gear (FIG. 6) are connected tothe propellers shafts through the gear couplings 1, 2 placed one insidethe other, compensating for the small size of the displacement of theaxes of shafts thus being capable to transmit high torques within therelatively small dimensions. Compensation of shaft misalignment isachieved by tilting gear sleeve with respect to the gear cage due tobacklash and the outer spherical surface of the teeth. The step-up gearincreases the speed of the slow-moving internal and external propellersstarting from 30 rpm (operation speed) to the generator operatingrotation speed.

The step-up gear is combined with the cylinder-shaped housing 10 ofwhich houses the bearing supports and the units 16, 17, 18 of theinternal and external driver shafts transmitting, the torque from thepropellers through the planetary gear system and sprocket transmissionto the generator shaft. Structurally the sprocket transmission and theplanetary gear of the internal shaft resemble the step-up planetary gearof the external shaft both of them have the same dimensions. In theplanetary gear heavy loads are applied to several satellites 5simultaneously, therefore, the size of the gears, and the size or thestep-up gear housing have optimum dimensions.

Supporting hearings 11, 12 of the external driving shaft are located inthe left half of the step-up gear casing. The left bearing assembly ofthe internal driving shaft 14 is embedded in the inner wall of the outerdriving shaft, whereas the right bearing assembly 15 is located in theright half of the step-up gear casing, respectively. The centralsprocket wheel with inner teeth 7 of the epicyclic outer shaft is fixedsecurely in the left half of the step-up gear 5, the satellites arefixed to the bearing supports 13 in the bores of the outer shaft, theguide they engage the sprocket teeth of the central large wheel with theinternal teeth and the particular small-size double-crowned wheel 6 withexternal teeth. The torque is transmitted through the second crown gearto the input shaft of the internal sprocket three-shaft step-up gear.The driver is a combined structure formed integrally with the shaft andcomprises one of the main links of the planetary transmission in whichthe axes of the satellites are fixed. The high precision of coordinationof the boles for the installation of satellites axes in the cagedetermines the distribution of the load among the satellites, thebearing capacity of the step-up gear, the noise level and vibrations.

Central wheel with inner teeth 7 of the planetary gear of the innershaft is fixed securely in the right half of the step-up gear casing,the satellites 5 are fixed on the supporting bearings 13 in the bores ofthe inner shaft within the driver guide and their teeth provide acoupling with the central large wheel and the internal teeth and withthe external teeth of the central small double-crown wheel 6. The torqueis transmitted through the second crown gear to the input shaft of theexternal three-shaft step-up gear.

The step-up gear is provided with a self-lubrication system comprisingthe oil cooler, oil pump and related units.

If the generator 20 in FIG. 4 is placed at the top of the tower then thegenerator rotor axis coincides with the central axis of the tower. Thethree-shaft gearbox output shaft transmits power to the shaft of thegenerator 19 through the intermediate transmission shaft 17, bevel gear18 and be rotating clutch.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the theoretical curves of wind energy efficiency of anideal wind turbine.

FIG. 2 shows decrease of the turbine speed with a decrease of the windspeed.

FIG. 3 shows variation of the speed of a special three-shaft planetarymechanism (the differential).

FIGS. 4 and 5 show the embodiments of double-rotor electric powerinstallations which offers new solutions different from the conventionalones.

FIG. 6 shows the step-up gear circuit.

FIG. 7 shows the blade bearing unit.

FIG. 8 shows the differential movement of units in the presentinvention.

FIG. 9 shows the diagram of the energy exchange between the main flowand the turbine.

FIG. 10 shows theoretical WEUC value of the ideal wind turbine based onthe ejection effect.

FIG. 11 shows kinematic diagram of the test stand.

FIG. 12 and FIG. 13 show the results obtained after the processing ofthe measurements and related calculations of basic tests.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Here the authors specify the basic design solutions of the noveldouble-rotor wind power installation.

1. The turbine blades comprise the rotating airfoil. The blade shellforming the aerodynamic surface is made of carbon-carbon compositematerial. The design is similar to an airplane wing: the spar, fibs,sheathing. The authors consider this blade stricture as novel. But themain thing is totally novel method for the calculation and design of theturbine. FIG. 1 shows the theoretical flow diagrams of the wind energycoefficients. Conventional curve is the A. Betz diagram. Maximumutilization of wind energy by Betz diagram is 0.5926, here the airpassage cross-section area of the wind turbine to the flow is about 67%of the swept surface area. In the existing wind turbine the air passagecross-section area is 92-94%. About 60% of the air flow passes theturbine blades and the energy of this part of the wind is not utilizedwith the turbine. The novel wind turbine which is offered here is basedon the use of E. Tikhonova's diagram shown in FIG. 1 (see Example 1). E.Tikhonova's diagram (or Tikhonova curve) is based on the assumption thatthe action of the air flow on the turbine leads to the effect of airejection, for air which passes through the turbine drive, this effect iscaused by air streams flowing around the turbine disk. As a result, theair pressure downstream of the turbine is reduced and the turbine outputpower increases.

The share of the passage cross-sectional area of 0.55 is accepted. Basedon the value of a passage cross-sectional area the optimum number ofblades their aerodynamic profile and geometry can be calculated.

Using this wind turbines design method the authors built model airturbines and studied their characteristics. Test results confirmed thehigh efficiency of these turbines, (See Example 2).

2. Structural diagram in FIG. 7 shows the blade bearing unit.

The shank end of the blade 1 is mounted in the sleeve 2 of the propellerhub 3. Inside the sleeve two sliding bearing are placed consisting ofceramic sleeves 4 and the friction surface on the shank end of theblade.

In the rotary sliding bearing of the wind turbine blade 5 solidlubricant is used which is based on metal dichalcogenides in combinationwith a ceramic sleeve. In conventional designs greases or liquidlubricants are used. Both require periodic changing which complicatesmaintenance and increases maintenance costs. There are also the problemswith leaking lubricant. The use of sliding bearings with solid lubricanteliminates a lot of problems in the operation: there is no need tosupply lubrication system for liquid oils or greases, no periodicmaintenance, no frequent replacement of lubricants.

3. Electric power generator is mounted in the tower but not on aturntable, as m the conventional wind turbines, the variant of thegenerator mounting is shown in FIG. 4.

The power generator is attached to the tower structure, its rotor axiscoincides with the axis of rotation of the turntable support bearing.Power cables running from the generator are laid out vertically on theinner surface of the tower. The reliability of the cables is ensuredwhereas the cables are not twisted when the platform is rotated to anyangle.

4. The rotor electric drive (see FIG. 4) is provided from the step-upgear through a bevel gear, the rotor axis coincides with the turntablebearing axis. The bevel gear casing is fixed to the turntable they bothrotate when wind vector is changing. An electric clutch is installedbetween the output shaft of the bevel gear and the electric generatorshaft to compensate some shaft misalignment. The bevel gear input shaftis connected to the a step-up gear with a transmission shaft.

5. The step-up gear is a dual gear mechanism. Its both circuits functionindependently. The torque of the second rotor of the turbine is appliedto the first circuit, the torque from the first rotor is applied to thesecond circuit.

The transmission is achieved by coaxial shafts up to the entrance of thethree-shaft gearbox. Each circuit consists of a planetary mechanism withthe inhibited crown gear wheel satellite and two sprocket wheels, withfixed axes. His structure has never been found or used before in theconstruction of wind power plants.

6. In this novel power installation there is a device which provides themost important function of the wind turbines. This three-shaft gear (seePos. 16 in FIG. 4). It is designed to maintain a constant speed of theoutput shaft when changing the speed of two coaxial input shafts. Thegearbox is a sprocket gear mechanism. One embodiment of this mechanismshown in FIG. 8 (the 3-shaft differential gear kinematics).

This planetary gear mechanism comprises two drives 5 and 7. In the cage5 the intermediate crown gear is secured. The driver 7 is rigidlyconnected to the inner input shaft 1 and the wheel 7 having the externalcrown gear 10. Satellites 8 are placed on the planetary driver 7.Between satellites 3 and 8 the intermediate gear rim 10 is mounted withinner and external sprocket teeth. Gear 6 with a fixed axis is used tochange the direction of driver 5 rotation with respect to the driver 7.The external input shaft 2 is coaxial with the shaft 1 it has a crown 3with internal toothing. The output central sprocket wheel 9 is engagedwith satellites 8.

In fact, this mechanism is a differential.

The movement of a conventional differential links can be expressedmathematically as:ω₃ =Aω ₁ +Bω ₂,  1)

where

A and B—constant coefficients depending on the mechanism's kinematicscheme;

ω₁—angular rotation speed of the input shaft;

ω₂—angular rotation speed of the other input shaft:

ω₃—angular rotation speed of the output shaft;

If the speed of one of the mechanism links, such as ω₂ increases at aconstant speed, than at ω₃ remaining constant the ω₁ rotation speeddecreases. When the ω₂ goes down the ω₁ speed increases. We assume thatthis differential is «positive».

If ω₃ speed remains constant, than changing either ω₃ or ω₂ rotationspeed, the differential movement expression shall be expressed as:Δω₁ +KΔω ₂=0,  1)

where

K—the constant coefficient which depends on the kinematic scheme of themechanism;

Δω₁ and Δω₂—variation of angular rotation speed;

In the proposed novel wind power installation the differential movementof units is totally different (see FIG. 8.):ω₃ =Aω ₁ −Bω ₂,  a)

or when Δω₃32 0Δω₁ =KΔω ₂  b)

If the speed of one shaft increases, it increases the speed of the othershaft. If the speed of the shaft is reduced, the speed of the othershaft is also reduced. This is a «negative» differentiation.

The scheme of the proposed mechanism and the differentiation method arenovel. No analogs are known. With such a mechanism one of their maintasks in wind power is achieved—to maintain constant rotation speed ofthe electric generator with the decreasing wind speed. No additionaldevices such as shift boxes, electronic frequency inverters shall berequired. The sine form of electric current is preserved withoutfrequency noise.

7. To eliminate the occurrence of dangerous infrasound frequencies inthe range of 0-12 Hz the number of blades in each rotor shall beselected on the condition that the number of the first rotor blades isz, and the number of the other rotor blades is (z+1).

8. An external rotor shaft 10 (see FIG. 5) is mounted on two ballbearings 11 and 12 that are placed in the rotary engine mountingplatform 2. The inner shaft 9 is also mounted on two hearings 6 and 12a. The inner shaft protrudes to 2.5-3 m from the end of sleeve 3 of theexternal rotor. Console extension of the inner shaft may reachsignificant values when the mass of the front hub with blades is 6-7ton. In order to improve the strength characteristics of the inner shaftthe external shaft is lengthened artificially by placing a cylindricalspacer 7, which is attached to the flange of the second hub with bolts.At the end of the spacers the rotary bearing 6 is fixed, With its insidediameter it is coincided and mounted on the sleeve 4. Bearing 6 becomesthe support of the inner front shaft. Inner shaft console length istherefore reduced to to 0.5 m instead of 3 m. The inner shaft 9 becomesmore rigid and durable with its spacer 7.

9. The proposed double-rotor wind power installation each rotor isindependent of the other, i.e, each one can rotate independently. Foroptimal use of the unique properties of «negative» differential aspecial control system has been developed for blades angles installationusing only 2 knobs. To prevent speed pulsations and rotation speed swinghave different blade rotor control rules are provided for thecontrollers. One knob adjusts the angle of the rotor blades in theirdirect dependence on the wind speed, as shown in:β₁ =f(υ),  1)

where

β₁—angle of the blades of one rotor;

υ—wind speed;

The feedback signal from the encoder of the rotation angle sensor whichmeasures the current position of the blade is fed to the wind speedmeasurement system.

The controller sets the other rotor angle β₂ to a value sufficient tostabilize the electric generator rotation speed, keeping it at constantlevel:β₂ =f(n ₂), at n _(r)=const,  1)

where

β₂—angle of the other rotor blades;

n_(r)—rotation speed (rpm) of the electric generator;

n₂—other rotor speed;

const—constant

Example 1

We propose a theory for calculating the WEUC (wind energy utilizationfactor) taking into account the ejection of turbine flow streams of themain air flow. FIG. 9 shows the aerodynamic configuration of theconsidered option.

We introduce an assumption that the pressure wave propagation velocityis close to the velocity of air flow, the diffusion and mass transferprocesses. This assumption is quite justified in the weather conditionsof the Earth's atmosphere.

The air flow runs over the turbine disk. Part of this flow with the massm₁ and initial cross-sectional area S₀ fells on the disc and the flowvelocity V₀ is slowing around the disc to V₁. The main air flow passesthe active working sections of the disc with a velocity V₀. Turbine flowhaving passed through the disk is ejected into the main air stream. Theturbine flow V₁ and V₃ of the mixed flow rate is less than the speed V₀of the main stream.

Due to the speed difference, the velocity vector of the sum of twopassing by streams shall be directed towards the flow with lower speed.The main flow will exponentially transmit us kinetic energy to theturbine as long as the turbine flow rate becomes equal to V₀. Thereforeit is better to set the limit:V ₄ =KV ₀≈0.97V ₀

This process causes the vacuum on the back side of the turbine disk P1*.We assume that the efficiency of the ejector mixing jets is 1.

FIG. 9 shows the diagram of the energy exchange between the main flowand the turbine.

flow number in the cross section «4» is;mV ₄ =ρS ₁ V ₄ ²

flow number in the cross section of «1» is:m ₁ V ₁ =ρS ₁ V ₁ ²

The difference in the number of movements, shall be, respectively:F ₄₋₁ =ρS ₁(V ₄ ² −V ₁ ²)

The difference of the flows between the sections «0» and S₁ is:F ₀₋₃ =m ₃(V ₀ −V ₁)=ρS ₁ V ₁(V ₀ −V ₃)

The total force acting on the turbine disk is:F _(Σ) =F ₄₋₁ +F ₀₋₁ =ρS ₁(V ₄ ² −V ₁ ²)+ρS ₁ V ₁(V ₀ −V ₁)

And the corresponding energy, working on the disc is:ΔW ₁ =F _(Σ) *V ₁

As a result, the formula for determining the energy efficiencycoefficient of the wind is as follows:

$\begin{matrix}{\xi = {\frac{{\Delta W}_{T}}{W} = {{2\frac{V_{1}}{V_{0}}\left( {K^{2} - \frac{V_{1}^{2}}{V_{0}^{2}}} \right)} + {2\frac{V_{1}^{2}}{V_{0}^{2}}\left( {1 - \frac{V_{1}}{V_{0}}} \right)}}}} & (11)\end{matrix}$

Exploring the function to the maximum we shall obtain the maximum WEUC:ξ≈0.999.  a)

The curve of

$\frac{{\Delta W}_{T}}{W}$changes shown in FIG. 10 (theoretical WEUC value of the ideal windturbine based on the ejection effect).

Whereas the

${\frac{V_{1}}{V_{0}} = \frac{S_{0}}{S_{1}}},$then the optimum area of the «live» cross-section of the turbine discshould be in the range of 0.5-0.75 of the total disk area.

Example 2

The test results of the experimental wind power installation withdouble-rotor wind turbine.

1. The Purpose of the Test

1.1 Determination of the Power Characteristics of the Wind Turbine.

1.2 Refinement of Methods of Calculation of Large Wind Turbines.

2. Test Object

2.1 Experimental Wind Turbine

nC-B-5 M.

Geometric and aerodynamic characteristics:

-   Turbine scheme: double-rotor, coaxial, with the opposite rotation of    the rotors;-   Rotor diameter—5 m,-   Number of blades per rotor—5 pcs.-   Blade aerodynamic profile—GA airfoil blades (W)-2 (NASA    terminology);-   Blade material—multilayer aviation plywood;-   Blade shape—rectangular, with constant chord;-   Chord length—0.12 m;-   Installation of the attack angle mechanism—rotation of die blade by    hand. Fixing the blades;

2.2 Kinematic Diagram of the Test Stand is Shown in FIG. 11.

Torque from the rotors of the wind turbine system 1 through V-belt andgears 2, 6 rotates the shaft of the electric generator 5. The generatoris mounted on ball bearings and is rotatable about the axis of itsrotor. The torque on the stator of the generator is applied through thebalancing lever to the scale 3. Damping of the system oscillations iseffected with the hydraulic damper 4. Power calculation is made usingthe torque and the rotation speed of the generator rotor, thecalculation method is described in InS-W-16/1. In addition, the power iscontrolled with dropping resistors 7.

3. Test Results

Tests were conducted in May and June 2008, The unit was installed on theflat roof of a 5-story building. Shading of the turbine for wind vectorwas not used.

Electrical connections were made in accordance with the procedureInS-W-16/1, Measurements were carried out at a steady wind conditions.The following measurements were made: the generator rotation speed, theload on the balancer lever, wind speed, temperature and barometricpressure, the date and time of measurement. All parameters were recordedin the operating log.

3.1 The measurements were made according to the procedure of procedureInS-W-16/1. The utilization of wind energy in the area swept with thewind turbine was calculated with correction for air density.

$\xi = \frac{{W_{mea} \cdot 1},23}{W \cdot \rho_{fact}}$Where W_(mea)—measured wind turbine power, W—maximum power of the wind,within the swept area; ρ_(fact)—measured air density at the time ofpower measurements.

The results obtained after the processing of the measurements andrelated calculations of basic tests are shown in the graphs, FIG. 12 andFIG. 13.

FIG. 12 double rotor wind turbine power vs the wind speed:

The line of actual power measurements

$\xi = \frac{{W_{mea} \cdot 1},23}{W \cdot \rho_{fact}}$

Calculated power values curve

Angular rotor speed of the wind turbine

Wind energy utilization coefficient

FIG. 13 Dependence of wind energy utilization coefficient

$\xi = \frac{{W_{mea} \cdot 1},23}{W \cdot \rho_{fact}}$on the Re number.

CONCLUSIONS

-   -   Received power values obtained during the test of the        experimental double-rotor turbine with counter-rotating rotors        demonstrate sufficient coincidence with the calculated power        values;    -   according to the test results, the dependence of wind energy        utilization coefficient in the form of

$\xi = {\frac{W_{mea}}{W} \cdot \frac{1,23}{\rho_{fact}}}$

-   -    on the Re number (FIG. 2) was established. With an increasing        Re number the wind energy utilization coefficient is increasing.    -   The test of the experimental wind turbine MS-W-5 it showed its        high efficiency;    -   It is advisable to develop a number of wind turbines on the        basis of double-rotor kinematic schemes. The use of a        differential mechanism with a variable transmission ratio is        recommended as a step-up gear;    -   Test results are recommend for use for the improvement of the        calculation method for wind turbines.

The Example 2 is based on the test results of the experimental of thewind power plant with double-rotor wind turbines obtained by theauthors.

What we claim is:
 1. A double-rotor wind power plant, comprising: a windturbine mounted on a tower with two coaxial wind propellers on arotating platform, a transmission, systems for controlling pitch anglesof blades and a position of the platform, an electric generator, whereina generator rotor with a vertical axis of rotation is situated on a topof the tower, and a stator of this generator is fixed to the tower, andan electric generator rotor axis extends vertically and coincides withan axis of rotation of the platform.
 2. A double-rotor wind power plantof claim 1, wherein a drive from the turbine to the generator is a bevelgear.
 3. A double-rotor wind power plant, comprising: a wind turbineplaced on a tower with two coaxial propellers on a rotating platform, atransmission, a control system for angle installation and position ofblades and a platform position, an electric generator, wherein a step-upgear is a double-gear mechanism assembled in a single package, eachcircuit of which transmits motion and torque from one of turbine rotorsindependently of movement of another circuit, that a kinematic diagramof the circuit is the planetary gear and a single-step gear.
 4. Adouble-rotor wind power plant, comprising: a wind turbine placed on atower with two coaxial propellers on a rotating platform, atransmission, a control system for angle installation and position ofblades and a platform position, an electric generator, wherein a coaxialthree-shaft sprocket gear is installed between a step-up gear and apower generator rotor, that a three-shaft gear kinematic diagram is madeaccording to a following conditionΔω₁ =K·Δω ₂, where ω₃=const, where Δω₁—a change of an angular velocityof an internal input shaft; Δω₂—a change of an angular velocity of anexternal input shaft; K—a constant factor, which depends on a gearkinematic scheme; Δω₃—a change in an angular velocity of an outputshaft; const—a constant.
 5. A double-rotor wind power plant, comprising:a wind turbine placed on a tower with two coaxial propellers on arotating platform, a transmission, a control system for angleinstallation and position of blades and a platform position, an electricgenerator, wherein a lengthening spacer is fixed on the external shaftof the turbine, at the end of which the front bearing the inner shaft isinstalled.
 6. A double-rotor wind power plant, comprising: a windturbine placed on a tower with two coaxial propellers on a rotatingplatform, a transmission, a control system for angle installation andposition of blades and a platform position, an electric generator,wherein a control algorithm of rotation angles of the blades of a firstrotor isβ₁ =f(υ), i.e., a positioning of the blade angle depends only on a windspeed, and a control algorithm of another rotor is n_(gen)=const, β₂=υarwhich means that a generator rotation speed is kept constant by changingangles of the other rotor blades, where β₁—is an installation angle ofthe first rotor; υ—is the wind speed; n_(gen)—is an electric generatorrotation speed; β₂—is another angle of the rotor; υar—is a variable.